1. Field of the Invention
The present invention generally relates to an electric field generating device, a light deflecting device, and an image display apparatus, and more particularly relates to an electric field generating device that forms in-plane electric fields by using potential gradients generated when an electric current is passed through a resistor, a light deflecting device that deflects light by using the electric field generating device, and an image display apparatus such as a projection display or a head-mounted display that includes the light deflecting device.
2. Description of the Related Art
Patent document 1 discloses an image display apparatus with a wide viewing angle. In the disclosed image display apparatus, the arrangement of liquid crystal molecules is changed by electric fields formed along the plane of an electrode substrate to achieve the wide viewing angle. In a light deflecting device used in the disclosed image display apparatus, parallel line electrodes are provided on the surface of one of two transparent substrates with a liquid crystal layer sandwiched between them. On the outside of the disclosed light deflecting device, multiple resistors for dividing the voltage supplied from a power supply are provided. The line electrodes are connected to connecting points between the resistors so that different voltages are applied to the line electrodes. The potential differences between the line electrodes generate electric fields between the line electrodes along the plane of the transparent substrate and thereby generate potential gradients in the liquid crystal layer. Thus, according to patent document 1, potential gradients are forcibly generated in the liquid crystal layer to obtain comparatively uniform electric field strengths throughout the disclosed light deflecting device.
Patent document 2 discloses a light deflecting device in which a dielectric layer made of a dielectric material such as glass or resin is provided between a liquid crystal layer and the surface of a substrate where line electrodes are formed to reduce discontinuous electric potential distribution and thereby to make electric fields in the liquid crystal layer substantially uniform.
[Patent document 1] Japanese Patent Application Publication No. 2004-286938
[Patent document 2] Japanese Patent Application Publication No. 2003-98502
A disadvantage of the light deflecting device disclosed in patent document 1 is that it is necessary to make the distance between the line electrodes longer to increase the effective area of the light deflecting device, and the longer distance makes it difficult to make electric fields between the line electrodes uniform. Especially, the directions and strengths of electric fields near the midpoint between the parallel line electrodes become non-uniform, making it difficult to achieve uniform optical deflection.
As described above, in the light deflecting device disclosed in patent document 1, a voltage is divided by the multiple resistors on the outside and the divided voltages are supplied to the line electrodes to generate electric fields along the plane of the transparent substrate. Because the resistors are provided on the outside, the size of the disclosed light deflecting device tends to become larger.
In the light deflecting device disclosed in patent document 2, a dielectric layer is provided between a liquid crystal layer and the surface of a substrate where line electrodes are formed to reduce discontinuous electric potential distribution and thereby to make electric fields in the liquid crystal layer substantially uniform. A disadvantage of the disclosed light deflecting device is that when the light deflecting device is activated, although it reduces diffraction of transmitted light, it may cause scattering of light and thereby dramatically decrease the contrast.